A very important thing to note about JSP custom tags is that they do not offer more functionality than scriptlets, they simply provide better packaging, by helping you improve the separation of business logic and presentation logic.

Some of the benefits of custom tags are:

They can reduce or eliminate scriptlets in your JSP applications. Any necessary parameters to the tag can be passed as attributes or body content, and therefore no Java code is needed to initialize or set component properties.

They have simpler syntax. Scriptlets are written in Java, but custom tags can be used in an HTML-like syntax.

They can improve the productivity of non programmer content developers, by allowing them to perform tasks that cannot be done with HTML.

They are reusable. They save development and testing time. Scritplets are not reusable, unless you call cut-and-paste reuse.

In short, you can use custom tags to accomplish complex tasks the same way you use HTML to create a presentation.